On Feb 17, 4:26*am, tom wrote:
http://www.theregister.co.uk/2011/02...radio_signals/

tom
K0TAR

perfectly logical and will probably result in a great patent... the
success in implementing it outside a well controlled lab environment
may be a problem though.

K1TTT has nailed it! Effecting a null that is deep enough to produce
something useful is difficult. In any case, the patent examiners will find
that the telephone people did something like this a long time ago. 73, Mac
N8TT

"K1TTT" wrote in message
...

On Feb 17, 4:26 am, tom wrote:
http://www.theregister.co.uk/2011/02...radio_signals/

tom
K0TAR

perfectly logical and will probably result in a great patent... the
success in implementing it outside a well controlled lab environment
may be a problem though.


J. C. Mc Laughlin
Michigan U.S.A.
Home:

On 2/17/2011 6:22 PM, J. C. Mc Laughlin wrote:
K1TTT has nailed it! Effecting a null that is deep enough to produce
something useful is difficult. In any case, the patent examiners will
find that the telephone people did something like this a long time ago.
73, Mac N8TT

J. C. Mc Laughlin
Michigan U.S.A.
Home:

One big difference is that the hybrid in a POTS phone doesn't want a
deep null. They want enough left of what is called "side tone" to give
feedback to the ear with receiver on it. If you don't they are
uncomfortable and also think the call has been dropped. It would be in
the -10 to -30dB range I'd guess.

On the other hand the null for this antenna array would need to be maybe
90dB or better to be really useful. Maybe with processing it could be
done with less, but I'd have to say, I don't know.

tom
K0TAR

On Thu, 17 Feb 2011 19:39:19 -0600, tom wrote:

On the other hand the null for this antenna array would need to be maybe
90dB or better to be really useful.

Here we have three (3) antennas, and as we all know they are not in
isolation.

Somewhere, there's a nearby (or near enough) overlooked reflective
surface that disrupts that oh-so-absolutely-necessary symmetry.

73's
Richard Clark, KB7QHC

On Feb 17, 7:01*pm, Richard Clark wrote:
On Thu, 17 Feb 2011 19:39:19 -0600, tom wrote:
On the other hand the null for this antenna array would need to be maybe
90dB or better to be really useful.

Here we have three (3) antennas, and as we all know they are not in
isolation.

Somewhere, there's a nearby (or near enough) overlooked reflective
surface that disrupts that oh-so-absolutely-necessary symmetry.

73's
Richard Clark, KB7QHC

About 25 years ago, I attended a conference on design methodologies
for blanking continuous (or high duty factor) signals in a military
environment. The benefit is to eliminate interference by your own
transmit signals to receivers, especially wideband EW/ECM receivers.
No discussion of twinned transmit antennas, though, but sample-and-
cancel techniques were prominent. Big problem: maintaining phase
linearity.

On Sat, 19 Feb 2011 23:33:03 -0800 (PST), "Sal M. Onella"
wrote:

Big problem: maintaining phase
linearity.

I was on duty aboard the USS Holland (my job, heading up the standards
lab) when one of the submariners rousted me out of my rack to make a
measurement - the last one before the captain could go out to sea.

I tumbled down the ladder (sometime in the early AM) to find a group
of techs huddled around a meg-Ohmmeter in the main passageway just aft
of Sherwood forest.

Now I add that significant detail because, as you mention about
maintaining phase linearity, every time a sailor shimmied past the
group to go forward, his movement would peg the meter in one direction
or the other. The guys were trying to measure a gigohm load in the
nuclear reactor. The disturbance of the local electric field was
enough to drive the resistance bridge wild. Any movement in its
vicinity was enough to do that. There was barely enough patience
among that group to let anything settle.

The sub couldn't move until they got at least 1 Billion Ohms, and when
I asked what the problem was (I was the pro from Dover there to rescue
their butts or the captain would keelhaul them), they said they were
several magnitudes of order off - too little resistance.

I hunkered down over the instrument, waited a couple of minutes before
the static fields settled and the instrument calmed, and I measured AT
LEAST a gigohm. "So what's the problem?"

"We need a billion ohms before we can certify the reactor is ready to
get underway!"

I looked at my measurement - easily a billion ohms, 1 gigohm (I
thought there wasn't that much resistance between us and the moon, but
I wasn't going to make that observation with the XO hunkered down
watching this, and the Old Man staring over his shoulder.).

"No, No! A BILLION OHMS!" came their plea when I pointed out the
measurement.

"What do you think a billion is?" I asked.

"We looked it up in the dictionary and its a million million."

I stood up and looked forward to crawling back into my rack. "That is
the English definition for billion. What you want is the American
definition for a billion which is a thousand million."

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Thu, 17 Feb 2011 19:39:19 -0600, tom wrote:

On the other hand the null for this antenna array would need to be maybe
90dB or better to be really useful.

Here we have three (3) antennas, and as we all know they are not in
isolation.

Somewhere, there's a nearby (or near enough) overlooked reflective
surface that disrupts that oh-so-absolutely-necessary symmetry.


All practical systems like this use some form of adaptive logic to fix
that. Usually, adaptive canceling is done in the receiver, because the
signal levels are lower, but in the 802.11 kind of world, with 100mW
linear transmitters, there's probably not much cost difference.

A different matter if you're running a kilowatt.

On Tue, 22 Feb 2011 09:54:53 -0800, Jim Lux
wrote:

Here we have three (3) antennas, and as we all know they are not in
isolation.

Somewhere, there's a nearby (or near enough) overlooked reflective
surface that disrupts that oh-so-absolutely-necessary symmetry.


All practical systems like this use some form of adaptive logic to fix
that. Usually, adaptive canceling is done in the receiver, because the
signal levels are lower, but in the 802.11 kind of world, with 100mW
linear transmitters, there's probably not much cost difference.

A different matter if you're running a kilowatt.

It only takes a couple of milliWatts (kiloWatts aside) to ruin your
day in competition for listening to microWatt signals. The desired
signal's transmitter antenna would have to be literally within the
near field of the active transmitter (and receiver's) antenna system.
At that point, we may as well use a land-line with hybrid bridges.

Software coming to the rescue for a hardware problem works only in
multi-million dollar projects (fly-by-wire avionics comes to mind).

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Tue, 22 Feb 2011 09:54:53 -0800, Jim Lux
wrote:

Here we have three (3) antennas, and as we all know they are not in
isolation.

Somewhere, there's a nearby (or near enough) overlooked reflective
surface that disrupts that oh-so-absolutely-necessary symmetry.

All practical systems like this use some form of adaptive logic to fix
that. Usually, adaptive canceling is done in the receiver, because the
signal levels are lower, but in the 802.11 kind of world, with 100mW
linear transmitters, there's probably not much cost difference.

A different matter if you're running a kilowatt.

It only takes a couple of milliWatts (kiloWatts aside) to ruin your
day in competition for listening to microWatt signals. The desired
signal's transmitter antenna would have to be literally within the
near field of the active transmitter (and receiver's) antenna system.
At that point, we may as well use a land-line with hybrid bridges.

Software coming to the rescue for a hardware problem works only in
multi-million dollar projects (fly-by-wire avionics comes to mind).


In these sorts of systems (the ones alluded to in the original news
story), all the signals are in one FPGA (in digital form) and the powers
are fairly low so all the RF stuff runs basically linear (DC to RF
efficiency isn't a huge deal on a 50mW transmitter next to a 10 Watt FPGA)

So it *is* a wireline hybrid bridge.. but done with numbers instead of
transformer windings.

The point I was getting at is that in these MIMO systems, there's
already multiple receive and transmit channels with substantial signal
processing going on. So it doesn't really matter much whether you do the
cancellation/null forming in the Tx or Rx side. If you can do some
clever canceling with Tx, and make it possible to use a cheaper Rx (or,
run full duplex without needing huge dynamic range/linearity in the Rx)
then that's probably a net good.

The technique proposed is very, very similar to one used to create
increased stereo separation ("headphone sound") from conventional stereo
speakers. You send a part of the Left channel signal to the right
speaker that just cancels the signal arriving at the right ear from the
left speaker. It's a very, very impressive effect.



73's
Richard Clark, KB7QHC

On Feb 17, 9:39*pm, tom wrote:
On 2/17/2011 6:22 PM, J. C. Mc Laughlin wrote:

K1TTT has nailed it! Effecting a null that is deep enough to produce
something useful is difficult. In any case, the patent examiners will
find that the telephone people did something like this a long time ago.
73, Mac N8TT

J. C. Mc Laughlin
Michigan U.S.A.
Home:

One big difference is that the hybrid in a POTS phone doesn't want a
deep null. *They want enough left of what is called "side tone" to give
feedback to the ear with receiver on it. *If you don't they are
uncomfortable and also think the call has been dropped. *It would be in
the -10 to -30dB range I'd guess.

On the other hand the null for this antenna array would need to be maybe
90dB or better to be really useful. *Maybe with processing it could be
done with less, but I'd have to say, I don't know.

tom
K0TAR

Normal level on a phone is about -25db I think sidetones are about 10
or 12db below that. Take that with a little salt my comm days are long
time past.

Jimmie